This invention relates to the field of taphole drilling in a shaft furnace. More particularly, this invention relates to a new and improved taphole drilling or opening device for shaft furnaces utilizing hydraulic power means and a uni-directional percussion instrument.
Presently, a method used in closing and opening the taphole in a shaft furnace comprises the positioning and extraction of a drill rod which is left inside the taphole between successive tappings. This relatively new method usually comprises the use of a pneumatic percussive working tool which exerts a bi-direction (i.e., forward and backward) action on the drill rod during the extraction thereof. The use of this recent drilling or taphole opening process has become increasingly widespread. Nevertheless, this process cannot be used in all circumstances. Accordingly, certain types of tapholes still necessitate the conventional method of drilling with a rotary percussion bit.
One particular disadvantage of this new taphole opening process is the fact that the rod can only be extracted from the taphole by means of a non-rotary percussive motion which includes both a forward and backward action. Thus, if it is desired to use a device or working tool which is capable of carrying out both the new taphole opening process and the conventional rotary drilling method, such a working tool must be capable of both drilling by rotation and exerting a percussive forward and backward (bi-directional) action.
Patent Application EP-A 0052248 corresponding to U.S. Pat. No. 4,497,379, all of the contents of which are incorporated herein by reference, discloses a hydraulic feed system which is especially designed for taphole drilling machines. The device disclosed therein permits the pneumatic tools to be replaced by hydraulic tools in taphole drilling devices. It is well known to those skilled in the art that hydraulic control offers numerous features and advantages over pneumatic tools. These advantages essentially consist of far greater power obtainable by hydraulic fluid as well as a considerable reduction in the noise produced thereby. Nevertheless, the hydraulic control system as disclosed in U.S. Pat. No. 4,497,379 has not been adapted to devices which are capable of opening and closing furnace taphole by both rotary percussive drilling and percussive bi-directional action. This situation has arisen because at present, there is no hydraulic bi-directional percussion tool.
Simple replacement or substitution of the pneumatic tool by a hydraulic tool, utilizing the added force of the hydraulic control as an aid in the extraction of a drill rod has also not been suggested or contemplated because, as prior art devices include a bar which is mounted at the end of a relatively long carrier arm, either the reaction in the latter will be too great or the arm (and the main pivot on which the arm moves) will have to be made very strong.